DE1285489B - Process for the production of steel pressure vessels consisting of parts welded together - Google Patents

Description

The invention relates to a method for the production of welded together Stable parts of existing pressure vessels. Find welded pressure vessels of this type for example as autoclaves and gas containers in the chemical industry and are preferably made of stainless austenitic steels.

The high pressures that the containers have to withstand require correspondingly high strength, which leads to considerable material costs, in particular when the container is made of stainless, austenitic steel. the Safety regulations for such vessels are strict and are regulated by the competent authorities Authorities closely monitored.

The object of the invention is, in compliance with the existing regulations the cost of manufacturing such pressure vessels from austenitic, stainless steel Steel degradation and a method of manufacturing pressure vessels from welded To create steel parts, with the help of which one can use pressure vessels of higher strength capable of producing the same wall thickness as before, or in compliance with the Strength regulations can do with less material expenditure.

To solve the problem, the invention is based on the fact from that the strength of austenitic steel increases significantly when it is subjected to tensile stress, which deforms the elastic yield point of the metal exceeds. Surprisingly, the stretchability is mostly only marginally reduced.

For tubes made of Cr-Cu steel, which are easy to weld, semi-hard and corrosion-resistant are, however, do not have an austenitic structure, it is known to have this if they are to be deformed by internal pressure into a shape of two or more Insert parts whose internal dimensions correspond to the final external dimensions of the pipe. Under The pipe expands under the influence of the internal pressure, whereby the yield strength of the Material exceeded and a permanent increase det: strength is achieved. There are precise details of how far the yield point should be exceeded not to be found in the literature., Furthermore, for the same material, the so-called "Fretting" known, with the pipe in question beyond its yield point against rigid forged clamps or against flexible clamps made of S, ow wires with a high elastic limit is expanded. As a result of permanent deformation of the pressure-treated pipe, this is firmly against the previously only pushed on Force on. The preload obtained is the same as that obtained, when the ferrules are applied warm and then shrink. like this with so-called "Hot-frozen" pipes is the case. An autofretted overpressed tube is deformed in this way against rigid ferrules, while in an overpressed autofretted Tube and the clamps are pressed over at the same time. They serve from essential higher quality material existing clamps in the form of one-piece rolled rings, hardened and tempered to replace the die into which the pipe is pressed will.

So these procedures basically require a form that the Stretching of the pipe clearly limited, and are therefore only suitable for the simplest Case of cylindrical pipes, but no- way to improve the strength properties of pressure vessels of any dimensions and size. Also, in all cases an additional heat treatment of the pipes is recommended, which apparently is practically indispensable is.

Furthermore, there is a method for work hardening of austenitic Steel known, which consists in passing through the interior of the steel part to be solidified pulling a mandrel, which has a corresponding oversize, through it under pressure. This measure is suitable; only for steel parts with uniform cylindrical Dimensions like pipes, and thus not for containers made up of different parts need to be welded together. In addition, a mandrel can be pulled through to widen a pipe only under the condition that the pipe is recorded accordingly. So you can only use relatively small, hollow bodies of revolution treat this way.

Finally, there is a method of creating biases in hollow bodies by pressing the hollow body using liquid or gas pressure known to beyond the yield point, which consists in the pressing in to carry out the heat and here, as well as during the subsequent cooling of the Pipes to adhere to such times that substantial degradation by the action of heat the stretching stresses generated by the plastic deformation during pressing are avoided will. So it is just a squeezing in the heat, without Incidentally, instructions on how to use the procedure in practice should be carried out, can be found in the literature.

According to the invention, the object is achieved in that at the manufacture of pressure vessels consisting of welded parts Austenitic stainless steel vessel below the recrystallization temperature is exposed to such a large hydraulic or pneumatic internal overpressure, that under free expansion of the vessel the weakest parts of the vessel become permanent Elongation of at least 10 / o but less than 10 / o can be cold-stretched.

None of the processes, some of which have been known for decades, has the Experts are encouraged to do this in the production of - pressure vessels from welded together To process parts made of stainless austenitic steel in the manner indicated.

So far there was namely in the professional world the opinion that any cold working an austenitic steel significantly reduces its corrosion resistance; so write z. B. the Swedish test standards for pressure receptacles expressly provide, that testing a stainless steel pressure vessel only at working pressure May be made in order to ensure a permanent stretching of the material during the pressure test to avoid. As a rule, it is precisely the corrosion resistance of pressure vessels has an extraordinary importance, this is apparently explained in the professional world existing prejudice against the cold deformability of such containers. Through in-depth laboratory tests the inventor has found that characterized by the cold working one austenitic stainless steel does not lower the corrosion resistance of the material is caused.

As a result, the Swedish state surveillance authorities granted the inventor an exemption for the pressure vessels manufactured according to the invention granted by the applicable test standards. The pressure vessels produced in this way from austenitic, Stainless steels have quickly found their way into practice and are being used all the time in increasing numbers.

It is of crucial importance that when carrying out the Cold stretching according to the invention does not include the container in any external shape so that when the internal pressure is applied, all parts of the vessel wall are stretched and thus a uniform strength is achieved.

The method of the invention has the particular advantage that containers any size can be solidified in the specified manner. Further becomes the greatest excess of the yield point and thus the greatest hardening reached just at the points where the container has the smallest wall thickness. This results in an automatic strength compensation of the various parts of the Pressure vessel.

The invention is explained in more detail below with reference to the figures.

F i g. 1 shows a welded cylindrical pressure vessel in front of the Pressure treatment; in Fig. 2 the same pressure vessel is shown in the finished state.

The container is z. B. made of a stainless steel with 18% chromium and 8 o / o nickel, i.e. made from a pronounced austenitic material. It consists of two curved end walls 10 and 11 and one of these with each other connecting, completely welded, cylindrical jacket 12 of uniform wall thickness. In the middle of each of the end walls 10 and 11 is a round hole with a welded-on cylindrical nozzles 13 and 14, while two cylindrical nozzles 15 and 16, respectively are welded into the shell part 12 in circular openings.

Each of the nozzles is initially at its outer mouth (Fig. 1) tightly closed by a welded-on, arched cover 18. In the middle of one the cover is welded into a connecting piece 17 for a pressurized water pump, not shown. When pressurized water is introduced into the container, it undergoes a maximum expansion its jacket in the circumferential direction approximately in the middle of the jacket part 12 of the Container, while the expansion of the end parts stiffened by the end walls 10 and 11 of the coat is slightly less. The elongation is measured and the supply of Pressurized water interrupted when the desired expansion value is reached.

The stretch that is suitable for each individual case depends primarily on on the properties of the material used. Usually one is residual or permanent elongation of the material on the weakest parts of the vessel is significant more than 0.2 O / o is required in order to achieve a considerable improvement in the strength properties of the material. For vessels that do not have an outer covering or Form are to be cold-pressed, one preferably chooses the cold-forming pressure -high enough to allow permanent stretching of the weakest parts from 1 to 2.3 o / o or 4%, at most 10%.

After cold stretching has taken place, the welded-on covers 15 cut away. In the case of the one shown in FIG. 2 are shown instead the nozzle 13 and 14 each have a ribbed tube 20, and the nozzle 15 is a straight tube 21 and a flanged elbow tube 22 is welded to the flanged connection piece 16. in the Remaining it should be noted that the wall thickness of the nozzle 13 and 15 is proportionate is dimensioned small, while the container wall all around the nozzle, however, by welding an additional sheet is reinforced and the wall thickness of the nozzle 14 is so great is that it alone provides sufficient stiffening of the adjacent part of the end wall guaranteed to the weakening caused by the hole in this end wall To take into account. Should the nozzles only be welded on after cold forming the reinforcements have to be dimensioned a little stronger.

As can be seen from FIG. 1, a sheet metal 19 is in the casing part 12 welded in, which is much stronger than the other cladding sheets. After Cold forming of the container, an opening is cut out of this sheet metal, into which a manhole ring 23 is welded (FIG. 2). This manhole ring is dimensioned so that it only takes into account the weakening caused by the hole wearing. The thickness of the plate 19, however, is so dimensioned that it is through the Welding compensates for the weakening or the cold stretching effect. The manhole cover is designated with 24 and the manhole bracket with 25.

A container of the type shown in the figures was made from a Material produced, the yield strength value of which was initially 25.0 kg / mm2. Through this, that in the container at room temperature water is pressed under such pressure found that the shell had a maximum permanent elongation of 2.3% the yield point increased by 7.5 kg / mm2 to 32.5 kg / mm2. Simultaneously there was only a slight decrease in the elasticity value of the material from 53 o / o to 49 0/0. The numerical values given relate to in this case on the material of the container before or after the pressure treatment. In the case described resulted from the application of the method according to Invention with the same safety factor a material saving of about 23 0/0.

Claims (1)

Claim: Process for the production of welded together Share existing pressure vessels made of steel by cold forming under pressure, d a -by characterized in that the pressure vessel made of austenitic stainless steel below the recrystallization temperature such a large hydraulic or pneumatic internal overpressure is exposed, that under free expansion of the vessel the weakest Vessel parts to a permanent elongation of at least 10 / o, but less than 10 O / o be cold-stretched.